Charge carrier foil

ABSTRACT

This invention relates to a flexible foil having a nonconducting selenium layer and an intermediate layer between the foil and the selenium. The intermediate layer consists of polyvinyl acetal with an addition of carbon black. Before depositing the selenium layer, the intermediate layer is polished. This intermediate layer results in excellent adherence of the selenium onto the flexible foil which can be used in copying machines.

United States Patent Esser et al.

[ Aug. 12, 1975 CHARGE CARRIER FOIL Inventors: Karl Esser, Stein; Robert Friedrich,

Nuremburg; John E. Segain, Gunzenhausen, all of Germany International Standard Electric Corporation, New York, NY.

Filed: Feb. 1, 1974 Appl. No.: 438,832

Assignee:

Foreign Application Priority Data Feb. 8, 1973 Germany 2306158 Feb. 8, 1973 Germany 2306159 US. Cl 96/1.5; 427/76 Int. Cl. G03g 5/00; B44d l/l6 Field of Search 117/216, 64, 201, 230;

References Cited UNITED STATES PATENTS ll/l960 Schaffert 96/1.5

3,226,253 12/1965 Gobrecht 1 17/201 3,467,548 9/1969 Straughan 117/106 R 3,615,413 10/1971 Fisher et al.... 96/15 3,639,121 2/1972 York 117/216 3,775,109 11/1973 Ohta et al. 96/1.5

FOREIGN PATENTS OR APPLICATIONS 912,837 12/1962 United Kingdom 96/1.8

Primary ExaminerCameron K. Weiffenbach Attorney, Agent, or Firm.lohn T. Ol-lalloran; Menotti J. Lombardi, Jr.; Vincent lngrassia [57] ABSTRACT 6 Claims, No Drawings CHARGE CARRIER FOIL BACKGROUND OF THE INVENTION The present invention relates to' a charge carrier foil consisting of a flexible conducting substrate with a nonconducting selenium layer and a conducting intermediate layer between the substrate and the selenium layer, and a process for preparing said foil.

In conventional electrophotographic copying machines, charge carrier plates in which a non-conducting selenium layer is arranged on a conducting substrate are used for forming the images. This selenium layer is charged electrostatically, and partly discharged by exposure with the desired image pattern, so that the image pattern will exist on the selenium layer in the form of a corresponding charge distribution. For making visible the charge pattern, an image powder, also known as toner, is applied to the selenium layer provided with the charge pattern, and is transferred from the selenium layer to a sheet of paper, where it is fixed.

Up to now, charge carrier plates in the form of rigid metal plates or of cylindrical metal drums have been used in electrophotographic devices. Since the surface of these plates and drums must correspond to the image to be reproduced, the size of the plates and drums is predetermined with respect to a certain size of image. The size of the plates or drums is thus determinative of the size of the electrophotographic apparatus, for example, the copying machine.

The overall size of such an electrophotographic apparatus could be substantially reduced if it were possible to use a flexible foil instead of the rigid plates or drums, with said foil being led inside the apparatus over rollers. Various proposals have already been published, suggesting how such charge carrier foils might be designed and produced. In practice, hoyvever, manufacture of such charge carrier foils always again had to be abandoned because the non-conducting selenium layer became cracked or because of spalling during the repeated bending-off of the foils. Therefore, considerable efforts have been made for improving adhesion of the selenium layer to flexible foils. One such known step resides in arranging between the flexible conducting substrate and the selenium layer an intermediate layer of a conductive material adhering well not only to the flexible substrate, but also to the non-conducting selenium layer. As the material for such a conducting intermediate layer, a variety of substances have been used up to now; for example, phenoplasts, cellulose lacquers, alkydes, phenol-formaldehyde resins, polyvinylcarbazole, urea melamine-aldehyde resins, polyester, polysulfides, polyurethanes, aminoplasts, polyvinyl alcohol, silicones, polystyrene, chlorinated rubber and other substances. All of these substances are rendered conductive, for example, by adding lampblack or graphite thereto.

However, it has been impossible to produce a nonconducting selenium layer having a sufficient service lifetime for use in electrostatic copying machines. Up to now it has not been possible with any of the hitherto conventional types of intermediate layer substances, to obtain charge carrier foils with a sufficiently long service life, i.e., where the selenium layer is prevented from spalling and from becoming cracked in spite of numerous bending-off processes during operation.

SUMMARY OF THE INVENTION It is the object of the present invention to provide a charge carrier foil with an intermediate layer which reliably prevents the spalling of the selenium during operation.

According to a broad aspect of the invention, there is provided a charge carrier foil comprising a flexible conducting substrate, a conducting intermediate layer on said substrate (said intermediate layer comprising polyvinyl acetal containing lampblack as an additive), and a non-conducting selenium layer arranged on said intermediate layer. It has proved that just this kind of intermediate layer substance is particularly suitable for improving the adhesion of the non-conducting selenium layer to the flexible substrate.

The above and other objects of the present invention will be better understood from the following detailed description.

DESCRIPTION OF PREFERRED EMBODIMENT Onto a clean, stainless and tape-shaped metal foil having a thickness of about 0.1 microns, for example, a steel tape, there is sprayed in a dust-free room and by using a blow gun, a conductive layer of lacquer for serving as the intermediate layer. This layer of lacquer consists of polyvinyl acetal as the basic substance to which there is admixed a share of lampblack and graphite for increasing the conductivity, and which contains ethyl acetate and methanol as the non-conducting solvent. The use of a non-conducting solvent offers the advantage that the lacquer conductance can be reduced to such an extent during the spraying process, that the lacquer may also be deposited in accordance with an electrostatic varnish coating method which is particularly suitable for largescale production. Owing to the dust-free surroundings, the surface of the layer of lacquer will be very even, thus guaranteeing an excellent coupling agent base for the photoconducting selenium layer to be deposited. The lacquer is preferably deposited onto the metal foil as a layer in the order of 1 to 2 microns thick and, by containing an approximately 10 per cent share of lampblack and graphite, has a conductance of 1.5 siemens. The same result has also been obtained in cases where the polyvinyl acetal contained an additional 10 per cent of lampblack or 10 per cent of graphite only. The conductance of the layer of lacquer should be kept appropriately within the limits of 1 to 10 siemens. By using a blow gun for spraying the layer a very uniform (constant thickness) layer will be obtained.

The addition of the lampblack causes the viscosity of the mass to increase. To compensate for this, the intermediate layer substance is provided with an addition of organic solvents, e.g. with a mixture of ethyl acetat and methanol. These solvents completely evaporate upon application of the intermediate layer, so as to secure the desired composition,

The thus coated foil is subsequently subjected to a heat treatment in a heating furnace at a temperature of C for a period of about 8 hours. Following this heating process and subsequent cooling, the layer of lacquer is polished by the application of pressure and a flexible superfine grinding machine. This further increases the surface smoothness of the layer of lacquer. Due to the polishing, the selenium layer can be charged to a higher voltage value. Compared with a nonpolished surface, the increase amounts to. as much as 250 volts. Thereafter, the photoconducting selenium layer which contains various additions, admixtures or dopings, but is preferably, however, provided with an addition of 0.5 per cent arsenic, may be deposited in the known manner in the form of a layer in the order of preferably 60 microns thick.

In cases Where the charge carrier foil is to be exposed to X-rays, it is of advantage to use a selenium layer containing an addition of up to percent by weight of a chemical element with a high atomic weight or of a chemical compound of such an element. Preferably, in this case, there is used a selenium layer containing an addition of lead or a lead compound. In this case the selenium layer may preferably be built up of partial layers; i.e., following the intermediate layer, there may be arranged a selenium layer of pure selenium on which there is deposited a selenium layer containing an addition of lead or a lead compound, and comprising as the top layer a selenium layer with an addition of arsenic amounting to 0.5 per cent.

Adhesive strength of the selenium layer when using the intermediate layer of polyvinyl acetal with an addition of lampblack and/or graphite has once been examined by pressing on and pulling off an adhesive foil and, secondly, by being subjected to a special bending test. The bending test was carried out in such a way that the charge carrier foil was welded to form an endless tape and placed over two rollers each having a diameter of 10 cm. Between the two rollers a tensile force amounting to about 10 kg was exerted upon the charge carrier foil. By driving the rollers at a speed of about 60 cm/sec., the foil was subjected to a permanent bending over the rollers. It has proved that even after 15,000 revolutions of the charge carrier foil around the rollers, there did not appear any detrimental variation in the selenium layer, e.g. crackings or spallings. Sticking on and pulling off an adhesive foil did not result in any selenium particlesbeing pulled off the layer. Froni this it will be seen that a charge carrier foil employing an intermediate layer of a material'as' suggested herein will provide for an excellent. adhesive strength of the selenium layer.

In order to achieve the conductivity of about 1.5 siemens, an amount of about 10 percent by weight of lampblack must be added to the polyvinyl acetal.

As stated above, surface polishing or grinding following heat treatment is preferably carried out with the aid of a flexible superfine grinding machine, but the use of additional polishing agents should be avoided. In depositing the-intermediate layer and in subsequent treatments, contamination of the intermediate layer surface must be carefully avoided. Further, any touching of the surface of the intermediate layer prior to the deposition of the selenium layer should be avoided.

. The selenium layer itself is deposited in the manner known per se by being evaporated under vacuum. As already outlined hereinbefore, it is of advantage for the selenium layer to contain certain additions, and the selenium layer may also be produced in the form of partial layers each having a different content of additions.

It is to be understood that the foregoing description of specific examples of this invention is made by way of example only and is not to be considered as a limitation on its scope.

What is claimed is:

1. A charge carrier foil comprising:

a flexible conducting metal foil;

a conducting intermediate layer on said metal foil, said intermediate layer comprising polyvinyl acetal containing lampblack as an additive; and

a non-conducting selenium layer arranged on said intermediate layer.

2. A charge carrier foil according to claim 1 wherein said intermediate layer has a thickness within the range of 1 to 2 microns.

3. A charge carrier foil according to claim 1 wherein 0.5 per cent by weight arsenic is added to said selenium layer.

4. A charge carrier foil according to claim 1 wherein the surface of said intermediate layer is smoothed prior to the application of said selenium layer.

5. A charge carrier foil according to claim 4 wherein the amount of lampblack additive is chosen such that the intermediate layer conductance will have a value between 1 and 10 siemens.

6. A charge carrier foil according to claim 5 wherein the conductance of said intermediate layer is 1.5 siemens. 

1. A CHARGE CARRIER FOIL COMPRISING: A FLEXIBLE CONDUCTING METAL FOIL, A CONDUCTING INTERMEDIATE LAYER ON SAID METAL FOIL, SAID INTERMEDIATE LAYER COMPRISING POLYVINYL ACETAL CONTAINING LAMPBLACK AS AN ADDITIVE, AND A NON-CONDUCTING SELENIUM LAYER ARRANGED ON SAID INTERMEDIATE LAYER.
 2. A charge carrier foil according to claim 1 wherein said intermediate layer has a thickness within the range of 1 to 2 microns.
 3. A charge carrier foil according to claim 1 wherein 0.5 per cent by weight aRsenic is added to said selenium layer.
 4. A charge carrier foil according to claim 1 wherein the surface of said intermediate layer is smoothed prior to the application of said selenium layer.
 5. A charge carrier foil according to claim 4 wherein the amount of lampblack additive is chosen such that the intermediate layer conductance will have a value between 1 and 10 siemens.
 6. A charge carrier foil according to claim 5 wherein the conductance of said intermediate layer is 1.5 siemens. 